Ultraviolet Excitation Dynamics of Nitrobenzenes

Lisa Saalbach, Nikoleta Kotsina, Stuart W. Crane, Martin J. Paterson, Dave Townsend

Research output: Contribution to journalArticlepeer-review

Abstract

Time-resolved photoelectron imaging was used to investigate nonadiabatic processes operating in the excited electronic states of nitrobenzene and three methyl-substituted derivatives: 3,5-, 2,6-, and 2,4-dimethylnitrobenzene. The primary goal was evaluating the dynamical impact of the torsional angle between the NO2 group and the benzene ring plane-something previously implicated in mediating the propensity for branching into different photodissociation pathways (NO vs NO2 elimination). Targeted, photoinitiated release of NO radicals is of interest for clinical medicine applications, and there is a need to establish basic structure-dynamics-function principles in systematically varied model systems following photoexcitation. Within our 200 ps experimental detection window, we observed no significant differences in the excited-state lifetimes exhibited by all species under study using a 267 nm pump and ionization with an intense 400 nm probe. In agreement with previous theoretical predictions, this suggests that the initial energy redistribution dynamics within the singlet and triplet manifolds are driven by motions localized predominantly on the NO2 group. Our findings also imply that both NO and NO2 elimination occur from a vibrationally hot ground state on extended (nanosecond) timescales, and any variations in NO vs NO2 branching upon site-selective methylation are due to steric effects influencing isomerization prior to dissociation.

Original languageEnglish
Pages (from-to)7174-7184
Number of pages11
JournalJournal of Physical Chemistry A
Volume125
Issue number33
Early online date11 Aug 2021
DOIs
Publication statusPublished - 26 Aug 2021

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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